1. Field
The present invention relates generally to wireless communications, and more specifically to techniques for optimizing the selection of wireless communications systems.
2. Background
With the deployment of a multitude of wireless technologies worldwide and support for these technologies in mobile multimode devices or entities, there is a growing need for seamless system selection toward the goal of global roaming. Furthermore, any particular geographic region may support mixed technologies and networks, such as 3rd Generation Partnership Project (3GPP) and 3rd Generation Partnership Project 2 (3GPP2) networks having WCDMA (Wideband Code Division Multiple Access) air interfaces, Global System for Mobile Communications (GSM), or other network technologies such as Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access (UTRA). World-mode user equipment (UE) devices support Single carrier (1X) radio transmission technology, CDMA2000 EVDO, CDMA2000 1xRTT, GSM and WCDMA.
A mobile multimode device that supports mixed technologies may include multiple databases that are used in selecting optimal networks within a technology. As an example, for 3GPP2 technologies, such as certain Code Division Multiple Access 2000 (cdma2000 or C2K) networks, a Preferred Roaming List (PRL) database which is stored at the User Equipment (UE) provides information about which system/network is preferred in a geographic region for that device. Whether predetermined or programmed via Over-The-Air (OTA) management protocols, the PRL contains information about the preferred networks and the order in which they should be selected for the user. PRLs for 3GPP2 technologies may be structured to have a table associated with each geographical region, which in turn contains a list of system descriptions keyed by System Identifier/Network Identifier (SID/NID) pairs and associated with an acquisition index. The acquisition index may be used as a pointer to an acquisition table which contains an indexed list of RF channels for channel acquisition purposes in the related system.
For 3GPP technologies, such as Global System for Mobile (GSM) and Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access (UTRA), a differently structured database list of preferred networks, termed Public Land Mobile Networks (PLMNs), is stored in a Subscriber Identity Module (SIM) or Universal Subscriber Identity Module (USIM) of the mobile device. The PLMNs in the database include a Mobile Network Code (MNC) that is used in combination with a Mobile Country Code (MCC) (also known as a “MCC/MNC tuple”) to uniquely identify a service operator using a 3GPP technology, such as GSM and UMTS public land mobile networks. Identification of a service operator may begin with the 3GPP approach to system selection based on PLMN lists, which may include 3GPP2 access technology identifiers (ATI), also known as Radio Access Technologies (RATs). A PLMN may identify and may be a concatenation of a MCC and a MNC.
When roaming through geographical locations, it is desirable that a multimode device seamlessly select the best available system, particularly when roaming across areas with different available access technologies (e.g., 3GPP and 3GPP2). When a world-mode device goes Out Of Service (OOS) due to loss of signal, current implementations calls for the device to scan 1x, DO, GSM and WCDMA. However, when a 1x carrier does not have roaming agreements with GSM/WCMDA carriers in the vicinity of the home country or the these networks do not exist in the home country, such as Verizon Wireless in the US, scanning GSM/WCDMA while in the home country is a waste of processing resources and power, and it delays the acquisition of service during power-up and the re-acquisition of service during OOS. Furthermore, during OOS, roaming charges paid by subscribers and carriers are accrued as soon as another non-home network is acquired even though the home network OOS may be transitory and the home network could be re-acquired after a short period of time at no cost. Typically the roaming partner is mostly determined by the position of roaming system in GEO/PRL rather than by the fee structure agreements with the most advantageous roaming partners.
There is therefore a need in the art for world-mode devices to manage technology selection for multimode roaming between existing access technologies, as well as possible future access technologies, in a manner that eliminates wasteful scanning for systems that are far away and considered out of range, i.e., faraway, and reduces roaming charges.